Alloy



PATENT OFFICE 2,096,201 ALLOY Donald w. Randolph, Flinhibfichlpassignor to General Motors Corporation, a corporation of Delaware No Drawing. Applicationiikugust-m, 1934, Se-

rial No. 740,537. In Germany and Canada April 16, 1934 2 Claims. totes-459) This is a continuation in part of my priorapplication Serial No. 667,502, filed April 22, 1933.

This invention has to do with alloys containing barium, a material of low work function, readily giving off electrons when energy is applied to it, such application of energy usually being in the form of either heat or electricity as in the conventional types of radio tubes. The invention also has to do with electron emitters made of such alloys.

In the prior application of Hugh S. Cooper, Serial No. 655,138, filed February 3, 1933, there is disclosed a method of making alloys of an alkaline earth metal, preferably barium, and nickel, which consists in employing a proportion of copper in the melt to hold the barium in solution. There are also disclosed in said application certain new alloys of the above description and electron emitters made of such new compositions.

As a result of independent but later work I likewise discovered the usefulness of copper in increasing the barium content of alloys containing nickel and barium and in addition have discovered that the addition of chromium to the melts produces finer grained alloys and gives to emitters made of such alloys advantages not possessed when chromium is omitted. Thus I have found that'radio tube filaments made of nickel, barium, copper, and chromium alloys may be operated for long periods without substantial deterioration at temperatures at which filaments of the same composition but with chromium omitted would rapidly deteriorate. Chromium appears to definitely inhibit evaporation of barium and so preserves the emitting surface. I

also found that electrodes made of the same alloy 479, granted July 25, 1933, that is, by melting the base metal or metals, wrapping the barium addition in foil or coating it to prevent oxidation and thereafter inserting it in the melt, holding the melt for a short time at an elevated temperature to permit thorough alloying and thereafter pouring. However while alloys of the desired high barium content could be made by this process, if the barium content was over about 25% the alloys were hard and brittle and could not be satisfactorily rolled or otherwise worked; i Such alloys were found to be high in gas content and so an effort was made to. eliminate gases therefrom.

Attempts were accordingly made to eliminate "g s by covering the melt with an atmosphere of 'COabr other inert gas but unsatisfactory results were obtained. Following this a number of trials were made with slags on the melt to exclude air, the barium being added through holes made in the slag. Here difi'iculty was encountered in obtaining a slag sufficiently sticky to form a gas tight seal. Best results were obtained with the use of a glass of the following composition, this glass being sticky over the range of temperature used in melting:

. Percent BaO 32.6 B203 18.7 K20 5.4 A1203 13 1 S102 40 2 The gas content of the metal was reduced by superheating under the .slag and continuing this until gas ceased to bubble through the slag. Thereafter the melt was cooled to pouring temperature, about .1% magnesium was added as a deoxidizer, followed by the addition of barium in the manner described. The melt was then held for a time varying from 30 seconds to two minutes depending on the amount of barium added, a longer time being required with the higher barium-contents. The slag was then removed and the metal poured into cold iron molds.

While better and more workable alloys were obtained by this process difliculty was nevertheless encountered'because of the tendency of the barium to react with the constituents of the slag producing oxide inclusions in the melt. Far more satisfactory results have been obtained by melting the base metals under vacuum, preferably in an induction furnace, and following the melting with further heat treatment under vacuum at temperatures several hundred degrees above the melting point to further reduce the gas content. When the melt has been sufficiently degassed, an inert gas is introduced into the furnace surrounding the melt and the barium is then introduced into the melt through the inert atmosphere. After allowing a sufiicient time for thorough alloying, the furnace, which is preferably mounted on pivots after the manner of a Bessemer converter, is inverted and the melt is poured into a mold enclosed in the furnace chamber and, of course, immersed in the same inert atmosphere. With this procedure the gas initially in the melt is first removed and all the operations thereafter are so conducted that oxidation and absorption of gases is almost entirely avoided. This method is to' be covered in a patent application about to be filed. Employing the method last described it has proven possible to produce alloys both of nickel Percent Nickel to 5 Copper 5 to 95 Barium 0.25to10.5

In general the higher the copper content, the higher the amount of barium that can be alloyed. To these alloys we have usually added a small amount of magnesium, approximately 0.1%, as a deoxidizer, but this may be omitted if desired for barium itself may serve the same purpose. Other known deoxidizers such as calcium are indicated as suitable for this purpose.

Manganese may likewise be added to the melt, but I have found it somewhat undesirable because of its high gas content. Other additions in the nature of diluents will readily occur to those skilled in metallurgy.

I have also used strontium in place of barium, and, while successful in securing homogeneous alloys of high strontium content, the emission has proven somewhat disappointing as compared to barium. For example, an alloy containing .8% strontium, 25% copper and the balance nickel was found to give but one-tenth of the electronic emission that was obtained from an alloy containing .8% barium, 25% copper and the balance nickel.

I have added varying amounts of chromium to the alloys described above in order to secure the advantage of the evaporation-inhibiting effect of chromium onthe barium in the alloy as well as increasedresistance to corrosion. The workability of the alloy is decreased by the addi-'-'- tion of chromium. Such alloys may be made in the manner above described within the following range of ingredients:

To these alloys the auxiliary materials men- 7 tioned above may-,likewisebe added if desired.

No difliculty is encountered in the melting procedure due to the addition of chromium although more gas is given oil. The addition of chromium does not greatly afiect the'alloying of barium. The chromium practically all alloys with the nickel, as copper-chromium alloys can only be made with great difliculty.

The described alloys have been made into filaments for radio tubes and into electrodes for gaseous discharge tubes such as are described and claimed in the prior application of Duffendack and Wolfe, Serial No. 716,972, filed March 23,

Where the alloy is used as an electrode 1934. in such tubes a chromium content of from to 2% has been found to be sufiicient to give the,

desired results.

In order to obtain the high rate of emission that is desired, filaments made of the described alloys are preferably oxidized and then activated by heating in a vacuum as described and claimed in the patent of Duflendack and Wolfe No. 1,909,- 916, granted May 16, 1933. In the testing of such emitters it has been found that those containing chromium can be operated at higher temperatures since the chromium definitely inhibits evaporation and so prevents destruction of the emitting surface. In the case of such emitters a chromium content of from 1 to 5% permits operation of the emitter at a temperature higher than in the absence of chromium. In some cases the emitter may be operated approximately C. hotter without loss by evaporation or decrease in emission due to breaking down in the emitting surface. As a consequence a somewhat increased output is obtainable from an emitter of a given size.

It is possible by varying the chromium content filament may be adjusted to a wide range of. values without changing its size.

I claim: I

1. An. alloy characterized by ready emission of electrons consisting of from 25% to 10.5% barium, from .1% to 25% chromium, from 5% to 95% copper and from 5% to 95% nickel.

2. An alloy characterized by ready emission of electrons and durability under emitting conditions consisting of from 25% to 10.5% barium,'

from .5 to 5% chromium, from 5% to 95% copper and from 5% to 95% nickel.

DONALD W. RANDOLPH. 

